Digital transmitter simulator

A digital transmit simulator for generating shift key modulated very low frequency signals for performance testing of at least one receiver comprising:

• means in the form of at least one readily changeable floppy disk for storing digital data representative of a modulation sequence and modulation mode used to test the receiver;
• means coupled to the digital data storing means for translating the stored digital data to compatible digital data modulation sequence signals and digital data modulation mode signals;
• means for providing inputs from a frequency standard for synchronization purposes;
• means coupled to the frequency standard providing means, the receiver and the translating means for generating shift keying modulated signals, the generating means including a modulator having a plurality of modulation modes coupled to the receiver, a mode register coupled to receive the translated digital data modulation mode signals from the translating means to create a selected actuation signal to initiate the modulator in a particular modulation mode and a data transition circuit coupled to the modulator to provide updated digital data to the translated data modulation sequence signals, the transition circuit including a static RAM having an operating instruction section responsive to operating instructions received from the translating means to provide actuating signals and an A memory and a B memory each responsive to information signals from the translating means to be alternately enabled to pass the information signals to the modulator and the data transition circuit also includes a universal shift register interposed between the static RAM and the modulator for feeding the information signals alternately from the A and B memories in a timed sequence according to a data clock rate signal coming from the modulator.